Fuel-water coalescers are commonly used in fuel systems to remove entrained water from hydrocarbon fuels. The removal of water is particularly important in diesel and gas turbine engines where entrained water can seriously reduce service life of fuel injectors and pumps. The typical coalescer includes an annular coalescing element formed of a series of superimposed layers of fibrous material constructed in a manner to allow a graded particle capture. The flow direction is from the inside-out, which creates a decrease in velocity as the diameter of the element increases. The decrease in velocity aids in coalescing the fine water droplets into larger globules that will fall by gravity along the outer surface of the element to the bottom of the unit for collection.
On the other hand, fuel filters used for trapping contaminants and particulate matter have traditionally utilized an outside-in flow. The outside-in flow provides a greater surface area on the outside of the element which reduces the tendency for the element to clog.
It may be desirable at times to substitute a coalescer or a combined filter-coalescer for the conventional filter. If the filter is connected to the engine block by connecting hoses, the change to the coalescer can be readily made by reversing the lines to the coalescer. However, most current fuel filters are of the spin-on type in which the filter is threaded into the engine block so that a simple hose line conversion to a coalescer cannot be made. In situations such as this, reversing the flow to accommodate the coalescer has been achieved by utilizing a flow reversing adapter which is positioned between the engine block and the spin-on coalescer. However, auxiliary adapters are expensive to produce, double the potential for leaks and take up valuable space that could otherwise be alloted to filtering or coalescing media. In addition, the use of an adapter makes it difficult to use the original filter element in conditions of emergency.